Neuro-Segmental Spinal Cord Reflexes

Front 1

What are the three characteristics of a reflex?

Back 1

1. Reflexes are graded
2. Duration of the motor response is usually limited
3. Restricted number of muscles involved in reflex

Front 2

Reflexes are movements caused by what type of input?

Back 2

Sensory input

Front 3

Does a larger stimulus result in a larger, smaller or equal response than a small stimulus?

Back 3

Larger response

Front 4

Duration of the motor response in a spinal cord reflex is limited by what?

Back 4

The duration of the stimulus

Front 5

What are two reflexes that are inborn?

Back 5

The moro reflex and the grasp reflex

Front 6

Are reflexes simple or complex?

Back 6

Both

Front 7

Can reflexes be modulated?

Back 7

Yes, reflexes can be suppressed or facilitated

Front 8

What are the five components of a reflex arc?

Back 8

1. Receptor
2. Afferent link
3. Reflex center
4. Efferent link
5. Effector

Front 9

What is the role of a receptor in a reflex arc?

Back 9

It records the stimulus and translates it into action potentials

Front 10

What is the role of an afferent link in a reflex arc?

Back 10

It conducts action potentials to the CNS

Front 11

Where can the reflex center be located?

Back 11

In the spinal cord, brain stem or cortex

Front 12

Reflexes can be facilitated or inhibited by what?

Back 12

Other receptors and afferent pathways and descending pathways

Front 13

What is the role of the efferent link in a reflex arc?

Back 13

It conducts action potentials to an organ that will produce a response

Front 14

What are efferent links in the reflex arc?

Back 14

Neurons with axons passing out of the spinal cord

Front 15

What is an effector in the reflex arc?

Back 15

Skeletal muscle, smooth muscle or cardiac muscle

Front 16

What are the four components of the myostatic reflex?

Back 16

1. Muscle spindle
2. 1a afferent nerve fibers
3. Alpha motor neuron and axon
4. Extrafusal muscle fiber

Front 17

what is another name for myostatic reflex?

Back 17

Stretch reflex or deep tendon reflex

Front 18

What does an extrafusal muscle fiber do?

Back 18

Produce a muscle contraction

Front 19

When is the stretch reflex activated?

Back 19

When extrafusal muscle (or tendon) is stretched

Front 20

What do 1a afferent nerves do when the stretch reflex is activated?

Back 20

Monosynaptically excite alpha motor neurons, excite 1a inhibitory interneurons and send signals up the spinal cord to higher centers in the brain

Front 21

Are 1a afferent nerves excitatory or inhibitory on alpha motor neurons?

Back 21

Excitatory

Front 22

What is the function of the 1b afferent reflex?

Back 22

It causes inhibition of homonymous and synergist muscles and excites antagonist muscles

Front 23

What are the components of the 1b afferent reflex?

Back 23

1. GTO
2. Ib afferent neuron
3. Interneurons
4. Alpha motor neurons to extrafusal muscle

Front 24

What is the sequence of events in the 1b afferent reflex?

Back 24

1. Tension in muscle increases
2. GTO activated
3. AP generated in 1b fibers
4. 1b fibers excitatory to inhibitory interneurons to agonist muscles and excitatory interneurons to antagonist muscles
5. As muscle tension increases, agonist muscles inhibited and antagonists activated

Front 25

Do GTOs and Ib fibers play a protective function?

Back 25

-GTO inhibits contractions that could be potentially injurious
-Protective function unlikely

Front 26

What is the most likely function of GTOs and Ib fibers?

Back 26

Provide information about muscle force to the CNS, help grade muscle contraction via inhibitory pathway and provide feedback for control of fine movements

Front 27

What is another name for the flexor withdrawal reflex?

Back 27

'Hot stove' reflex

Front 28

What is the sequence of events in the flexor withdrawal reflex?

Back 28

1. Cutaneous pain receptors activated
2. A-delta afferents to spinal cord
3. Polysynaptic connections to interneurons that excite flexor muscles and inhibit extensor muscles

Front 29

What is the sequence of events in the flexor withdrawal reflex of the lower extremity?

Back 29

-Flexor muscles activated
-Contralateral extensor muscles activated to keep from losing balance
-Contralateral response accomplished by interneuronal pathway that crosses the midline of the spinal cord

Front 30

What are the two types of inteneurons that modulate activity?

Back 30

1. Ia inhibitory interneurons
2. Renshaw cells

Front 31

Where are Ia inhibitory interneurons found?

Back 31

In the spinal cord

Front 32

What do Ia inhibitory interneurons synapse with? Are the synapses inhibitory or excitatory?

Back 32

1. Ia afferent-excitatory
2. Alpha motor neurons-inhibitory

Front 33

What is the function of Ia inhibitory interneurons?

Back 33

Allows higher centers of the CNS (including cerebral cortex) to:
1. Inhibit antagonist while activating agonist (reciprocal innervation)
2. Modulate the activity that passes through a reflex arc
3. Modulate activity of agonist and antagonist motor neurons

Front 34

How do higher centers of the CNS modulate activity of agonist and antagonist motor neurons?

Back 34

-Inhibit Ia inhibitory interneuron
-Antagonist muscle can now be activated
-Agonist and antagonist muscles can be active at the same time or co-contract

Front 35

When would co-contraction of muscles be necessary?

Back 35

For stability during holding contractions (holding a cup) and important for postural muscles

Front 36

What is the purpose of inhibitory interneurons?

Back 36

They allow the CNS to have more subtle control of motoneuron activation
-More complex combinations of activation of agonist and antagonists
-Enable spinal centers to more automatically modulate

Front 37

Renshaw cells receive input via what structure? Is it inhibitory or excitatory?

Back 37

Recurrent collateral branch of alpha motor neuron; excitatory

Front 38

What is recurrent inhibition?

Back 38

Inhibitory input back onto the alpha motor neuron that drives it and alpha motor neuron of synergistic muscles

Front 39

What is the function of Renshaw cells?

Back 39

-They inhibit Ia inhibitory interneurons
-Allow alpha motor neuron to the antagonists to be excited
-Allows contraction of the agonist and antagonist muscles together (co-contraction)

Front 40

Can all reflex pathways be modulated?

Back 40

Yes

Front 41

How are all reflex pathways modulated?

Back 41

1. Activity in pathway enhanced
2. Activity in pathway inhibited